(1) Field to which the invention relates
The present invention relates to an interference optical measuring device comprising a light source, a beam splitter, two component beam optical paths and a sensing radiation sensor for a centrifuge with a multiple hole rotor, which has holes for receiving a respective sample cell or a counter balance, which on rotation of the rotor successively pass through the component beam optical paths and at one respective position simultaneously lie in both component beam optical paths, and further an arrangement for producing a position signal, which indicates that a selected hole is located in the particular position, in which it lies in the two component beam optical paths, and a control arrangement which activates the measuring device in the predetermined position of the selected hole briefly.
(2) The prior art
The U.S. Pat. No. 3,391,597 and a SB-200 Manual of the Spinco Division, BECKMAN INSTRUMENTS, INC. Palo Alto, Calif. for the E model ultracentrifuge describe analytical ultracentrifuges with multiple hole rotors, in the case of which changes in concentration in samples, which are located in sample cells in the multiple hole rotor, can be measured while the centrifuge is operating by means of an interference optical measuring device. The latter comprises two component beam ray paths placed in succession in the direction of rotation of the rotor of the centrifuge and which are successively completed for the passage of light by the holes of the rotor (or observation windows of the sample cells or apertures in a counter balance) and in a certain rotor position they both simultaneously pass through a respective hole. In this position the ray beams from the two component beam optical paths can interfere with each other and a measurement can be carried out.
In the case of a previously proposed centrifuge of this type it is possible to use a so called "multiplexer" to select and measure one of several cells in the multiple hole rotor. For this purpose a position signal is produced in the ultracentrifuge, for example by means of an optical encoding ring, which indicates that the selected hole or a sample-free hole, serving for reference measurements, and which contains a counter balance, is located in the optical ray path of the measuring device.
The position signal used in practice persists until the interference optical measuring device on the one hand is already enabled, just when the one component beam optical path has been optically completed by the selected hole and on the other hand it is only switched off, after one of the component beam optical paths has been interrupted by the rotor again. Since the ratio of the signal to noise is impaired, if the sensing radiation sensor should receive light only from one component beam optical path, which alone cannot produce any interference, there has been a suggestion in the prior art to operate the interference optical measuring device with pulsed optical means in such a manner that the illumination is limited to the respective rotor position, at which the two component beam optical paths pass through the selected hole (Anal. Biochem. 48 (1972), pages 588 to 604; pages 605 to 612).